Updating Github actions and files to use main branch. (#1023)

(Cherry picked from commit dc291c2)

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
       - '*'
   push:
     branches:
-      - master
+      - main
       - opendistro-*
 
 jobs:

CONTRIBUTING.md

@@ -22,7 +22,7 @@ When filing an issue, please check [existing open](../../issues), or [recently c
 ## Contributing via Pull Requests
 Contributions via pull requests are much appreciated. Before sending us a pull request, please ensure that:
 
-1. You are working against the latest source on the *master* branch.
+1. You are working against the latest source on the *main* branch.
 2. You check existing open, and recently merged, pull requests to make sure someone else hasn't addressed the problem already.
 3. You open an issue to discuss any significant work - we would hate for your time to be wasted.
 

README.md

@@ -1,5 +1,5 @@
-[![CI](https://github.com/opendistro-for-elasticsearch/security/workflows/CI/badge.svg?branch=master)](https://github.com/opendistro-for-elasticsearch/security/actions)
-[![codecov](https://codecov.io/gh/opendistro-for-elasticsearch/security/branch/master/graph/badge.svg)](https://codecov.io/gh/opendistro-for-elasticsearch/security)
+[![CI](https://github.com/opendistro-for-elasticsearch/security/workflows/CI/badge.svg?branch=main)](https://github.com/opendistro-for-elasticsearch/security/actions)
+[![codecov](https://codecov.io/gh/opendistro-for-elasticsearch/security/branch/main/graph/badge.svg)](https://codecov.io/gh/opendistro-for-elasticsearch/security)
 
 # Open Distro for Elasticsearch Security